I. Field of the Invention
The invention relates generally to shields used in the protection of electrical components from electromagnetic and radio frequency interference (EMI/RFI). More particularly, the invention relates to shield clips and methods of providing EMI/RFI shielding in communication devices.
II. Description of the Related Art
Electrical components, such as resistors, capacitors, and semiconductor components, are often subjected to undesirable emissions, such as EMI/RFI, from neighboring emitting components. These emissions interfere with the operation of such components by temporarily altering or distorting their essential characteristics and, consequently, performance. Several methods are used to protect and shield components such as these from EMI/RFI occurring in proximity to a printed circuit board (PCB). A first method involves directly soldering an RF shield to a ground plane of a PCB around RF emitting components. A second method involves the use of shield clips coupled to the ground plane of a PCB to which an RF shield is permanently attached. A third method involves the use of removable RF shields attached to shield clips coupled to the ground plane of a PCB. FIGS. 1 and 2 illustrate a front elevation view of two such conventional RF shield clips.
Several problems are associated with the applicability of these shielding devices and methods. For example, in the first method, it is often time consuming to solder RF shields to the ground plane of the PCB, thereby making the manufacturing process costly and inefficient. More importantly, by soldering RF shields to the PCB, it is highly cumbersome and often impossible to troubleshoot, repair, or replace components that are covered by the RF shield. In the second method, the permanent attachment of the RF shield to the shield clips subjects this method to problems similar to those associated with the first method.
In the third method, the shield clips often lose their spring tension that makes them unable to maintain a shield cover in place. As illustrated in FIGS. 1 and 2, two shield clips 100 and 200 are shown, each comprising a pair of side walls 107, 109 and 207, 209. Each pair of side walls is spring biased inwardly toward the other, and bends outwardly in response to introduction of a shield cover between the walls, thus permitting insertion of the shield cover wall, e.g., a shield wall 115. The spring tension of each pair of side walls attempts to keep the shield wall 115 in place over time. However, these shield clips tend to lose their spring tension and, hence, lack a sufficient grip to keep the shield wall 115 in place. To minimize the effects of lost tension, the shield clip 100 includes a locking latch 113 that locks the shield wall 115 in place. The shield wall 115 includes one or more grooves, each groove suitable for receiving the tip of the locking latch 113. The lock latch 113 inserts into one of the grooves and, by virtue of its tension, locks the shield wall 115 in place. The use of the latch 113, however, makes the shield cover more cumbersome and difficult to remove. Thus, having such a locking mechanism may defeat the purpose of maintaining removability of the shield cover.
Additionally, the soldering reflow may come in contact with the lower edge 111 of the shield wall 115 thereby making the shield cover difficult to remove from or become stuck in the shield clip. Consequently, troubleshooting, repairing, or replacing one or more components covered by the soldered RF shield is impaired. For further details on removable RF shields, reference is made to U.S. Pat. No. 5,577,268 issued to Ho et al., which is incorporated by reference.
Another problem associated with RF shielding involves the use of a large number (e.g., 10-50) of small RF shields. Typically, these RF shields are rectangular in shape with a width in the range of 1-5 millimeters (mm) and a length in the range of 1-5 mm. Mounting such a large number of small RF shields on the PCB increases the manufacturing time of the PCB and, consequently, implicates manufacturing costs.
Therefore, there is a need in the RF shielding technology to provide a removable shield that may be placed on PCBs using reliable shield clips, despite repetitive removal of the RF shield. Additionally, the RF shield should be designed to ensure separation from the solder reflow to ensure ease of removal from the PCB.